An antenna device capable of transmitting and receiving different polarized waves allows to select an appropriate polarization to transmit and receive, thereby making it possible to perform communication even in a case where polarization of a radio wave that the antenna device receives is changed or in a case where the antenna device changes its orientation, as in the case of mobile phones. Such a technique is known as polarization diversity.
Patent Literature 1 describes antenna devices that attain polarization diversity by use of one (1) antenna element. FIGS. 20 and 21 illustrate the antenna devices described in Patent Literature 1.
An antenna device 10 illustrated in FIG. 20 includes an antenna element 1020 having an X shape. In a case where the antenna element 1020 is fed by a feeding portion 1030, a high-frequency electric current flows in the antenna element 1020 in a direction indicated by an arrow 1031 (see (a) of FIG. 20). Meanwhile, in a case where the antenna element 1020 the antenna element 1020 the antenna element 1020 is fed by a feeding portion 1040, high frequency electric current flows in the antenna element 1020 in a direction indicated by an arrow 1041 (see (b) of FIG. 20).
An antenna device 11 illustrated in FIG. 21 includes an antenna element 1120 having an L shape. The antenna element 1120 has a center part 1150 which is grounded. In a case where the antenna element 1020a is fed by a feeding portion 1130, high frequency electric current flows in the antenna element 1020 in a direction indicated by an arrow 1131 (see (a) of FIG. 21). Meanwhile, in a case where the antenna element 1020 is fed by a feeding portion 1140, high frequency electric current flows in the antenna element 1020 in a direction indicated by an arrow 1041 (see (b) of FIG. 21).
Thus, the antenna devices described in Patent Literature 1 is configured to change the direction of the flow of the high frequency electric current in the antenna element by changing where the feeding portion is provided, so as to switch main polarization of the radio wave to be transmitted or received. Such antenna devices attain polarization diversity by use of one (1) antenna element, and therefore can advantageously reduce cost, space, and the like required for the antenna element.